Densified nitrocellulose-hydrocarbon product and process of manufacture



' ate 3,234,253 Patented Nov. 8, 1956 3,284,253 DENSIFIED NITROCELLUL'GSE HYDROCARBON PRODUCT AND PRGCESS OF MANUFACTURE John G. Enders Westfield, and Daniel S. Wiit, Cranford, NJ, assignors to Hercules Incorporated, a corporation of Delaware N Drawing. Filed Aug. 27, 1963, Ser. No. 304,985 14 Claims. (Cl. 1492) This invention relates to nitrocellulose manufacture, and more particularly to a novel nitrocellulose product and to the process for producing the same.

Nitrocellulose in the dry state is extremely hazardous and dangerous. Consequently, all commercial nitrocellulose is supplied to the trade wet with a non-solvent liquid in order to minimize fire hazards during storage, shipping and handling of the nitrocellulose. For most purposes, the Wetting liquid employed is an alcohol such as ethanol, isopropanol or butanol. However, for certain specialty uses the nitrocellulose may be supplied wet with water, instead of with an alcohol. There are, however, important uses for nitrocellulose where it would be highly desirable economically to employ nitrocellulose wet with a volatile hydrocarbon liquid such as toluene rather than with an alcohol or water. Heretofore, however, methods which have been proposed for producing nitrocellulose wet with a volatile hydrocarbon liquid have been deficient in variou respects.

For example, it has been proposed to produce a hydrocarbon wet nitrocellulose by placing fibrous nitrocellulose wet with water in a still containing an excess of a volatile hydrocarbon liquid, and then subjecting the contents of the still to azeotropic distillation either at atmospheric or reduced pressure until substantially all of the water ha been removed from the nitrocellulose.

However, the resulting fibrous nitrocellulose wet with hydrocarbon liquid retains far too much hydrocarbon liquid, and must then be subjected to pressure in a conventional hydraulic press to squeeze out excess hydrocarbon liquid, after which the compressed blocks must be broken and fluffed up for packing into barrels. The above pressing and block breaking steps are inherently quite expensive and hazardous. Moreover, since the bulk density of fibrous nitrocellulose is quite low, the nitrocellulose must be packed into the barrels by compressing it with a hydraulic ram to increase barrel loadings, in order to reduce shipping costs. As a result of compression in packing, nitrocellulose users find the fibrous material quite difiicult to unload from the barrels. An additional disadvantage of fibrous nitrocellulose is the tendency to agglomerate and form large slow-dissolving lumps when added to solvents in certain types of dissolving equipment.

It is also known that fibrous nitrocellulose, conventionally dehydrated with an alcohol such as ethanol, isopropanol, or butanol can be further processed to produce a substantially hydrocarbon-wet nitrocellulose by displacing the alcohol with a hydrocarbon liquid in an additional series of steps comparable to the alcohol dehydration steps. With this method a portion of the first dehydrating medium, namely, the alcohol, is usually retained at the end of the operation, requiring recovery equipment or loss of alcohol which is undesirable for certain applications. Moreover, the double displacement processing required is obviously much too expensive, and is hazardous as noted hereinbefore, and the resulting product is also subject to the additional disadvantages of being diflicult to unload from barrels and has undesirable dissolving characteristics as noted hereinbefore.

It is an object of this invention, therefore, to provide a hydrocarbon-wet nitrocellulose of improved form which can be transported more economically, unloaded from barrels more easily, and which has improved dissolving characteristics in comparison to conventional fibrous nitrocellulose.

Another object of this invention is to provide a nitrocellulose product of improved form which in the presence of excess hydrocarbon liquid drains freely to produce a hydrocarbon-wet nitrocellulose wetted with between about 10% and about 40% by weight of sorbed hydrocarbon liquid.

It is a further object of this invention to provide an improved process for producing a hydrocarbon-wet nitrocellulose which -has economic and procedural advantages over prior art methods, and which substantially overcomes the limitations and deficiencies of prior art methods.

These objects and others are accomplished in accordance with the present invention which, generally described, comprises contacting a slurry of fibrous nitrocellulose with agitation in a heated aqueous bath with an organic liquid solvent which has active solvent power for said nitrocellulose, regulating the amount of said solvent between about 0.3 part and about 2 parts by weight per part of nitrocellulose to soften and destroy the fibrous structure of said nitrocellulose without dissolution of said nitrocellulose, removing substantially all of said solvent by distillation while continuing agitation to transform the softened nitrocellulose into smooth, hardened, densified, irregular granule having a free-draining physical structure capable of holding between about 10% and about 40% by weight of sorbed nonsolvent liquid, separating excess water from the resulting hardened nitrocellulose granules to produce nitrocellulose granules wet with sorbed water, thereafter substantially displacing sorbed water from the nitrocellulose granules by distillation in the presence of an excess of volatile hydrocarbon liquid, separating excess hydrocarbon liquid, and recovering nitrocellulose granules wetted with between about 10% and about 40% by weight of sorbed hydrocarbon, based on total weight.

The terms sorb and sorbed are used herein in the description and claims in their usual sense to mean the ability of the nitrocellulose to take up and hold a liquid, either by adsorption or absorption, or by a combination of adsorption and absorption, substantially independent of the force of gravity.

In a preferred embodiment for practicing this invention, water-wet fibrous nitrocellulose, after conventional treatments for stabilization and viscosity adjustment, is mixed and agitated with a large quantity of water to produce an aqueou slurry of nitrocellulose. Nitrocellulose solvent is then added with agitation to the aqueous nitrocellulose slurry heated approximately to the boiling point of the water-solvent azeotrope in an amount sufiicient to change the physical form of the nitrocellulose from fibrous to smooth, hardened, densified, irregular granules having a degree of densification corresponding to a bulk density between about 20 and about 40 pounds per cubic foot, dry basis, upon removal of the solvent by distillation. This is a critical feature of the invention, for the degree of densification achieved by solvent treatment and removal governs the free-draining characteristics of the nitrocellulose, and thus the capacity of the nitrocellulose to hold the desired amount of hydrocarbon liquid in the sorbed state for the purposes of this invention. Too little densification results in a product which will retain an excessive amount of sorbed hydrocarbon liquid, while too much densification results in a product which will retain an insufficient amount of sorbed hydrocarbon liquid.

In this process the organic solvent is partitioned to the nitrocellulose which is softened and the fibrous structure thereof is destroyed. However, the nitrocellulose is not dissolved, and the softened particles thus produced are hardened by boiling off substantially all of the solvent. Agitation is maintained until hardening is complete in order to minimize agglomeration during hardening. Excess water is then separated by any convenient means, such as by gravity drainage, centrifugation, or the like, and the nitrocellulose granules wet with sorbed water are then subjected to ordinary or azeotropic distillation in the presence of an excess of volatile hydrocarbon liquid, such as toluene or a petroleum distillate, until sorbed water has been substantially displaced by hydrocarbon liquid. Excess hydrocarbon liquid is then separated by any convenient means, such as by gravity drainage, centrifugation, filtration, or the like, to produce the novel hydrocarbon-wetted nitrocellulose of this invention.

The hydrocarbon-Wetted product produced by the process of this invention is composed of small, hard, densified irregular particles of nitrocellulose having a diversity of particle sizes, and which when magnified appear to have smooth, glazed surfaces. As noted above, these particles have a degree of densification corresponding to at least about 20 pounds per cubic foot and not more than about 40 pounds per cubic foot, dry basis, and are Wetted with between about 10% and about 40% by weight of sorbed hydrocarbon liquid. The hydrocarbon-wetted product of this invention is further characterized by being free flowing, fast dissolving, and relatively incompressible. The chemical characteristics of the product of this invention are apparently the same as conventional nitrocellulose, since no chemical action is involved in the process of producing said product.

The general nature of the invention has been set forth and the following examples are presented as specific illustrations thereof.

EXAMPLE 1 One hundred fifty (150) parts by weight, dry basis, of fibrous, water-wet nitrocellulose, 11.5% nitrogen by weight, 4.8 seconds ASTM inch falling ball viscosity, and having a bulk density, dry basis, of 13.3 pounds per cubic foot, were mixed with sufficient water to prepare an aqueous slurry containing by weight of nitrocellulose. This slurry was heated and agitated in a closed vessel equipped with a turbo blade agitator, an inlet for solvent introduction, a thermometer, a condenser, and heated by sparge steam. When the temperature in the slurry reached 64 C., methyl ethyl ketone in an amount equal to one part by weight for each part by weight of nitrocellulose was added to the agitated slurry through the solvent inlet. Heating and agitation were continued, and the solvent was substantially all removed by azeotropic distillation at atmospheric pressure. The temperature in the slurry at the end of the distillation was 94 C. During this solvent treatment the fibrous nitrocellulose was transformed into small, smooth, hardened, irregular particles having a bulk density, dry basis, of 24 pounds per cubic foot.

Excess water was gravity drained from the hardened nitrocellulose particles, and the resulting water-Wet nitrocellulose particles were slurried in toluene in the same vessel employed for the solvent treatment. Vacuum equal to 10.5 inches of mercury was applied to the vessel, and the toluene slurry of nitrocellulose particles was heated and agitated. Azeotropic distillation commenced when the temperature in the slurry reached 67 C. and was discontinued when the distillate no longer separated into a water phase and a toluene phase, thus indicating substantial displacement of sorbed water from the nitrocellulose particles by toluene. The temperature in the slurry at the end of the distillation was 92 C. The toluene slurry of nitrocellulose particles was then subjected to gravity drainage to remove excess toluene, and substantially all excess toluene had drained off after two hours. The resulting toluene-wet nitrocellulose product contained 70% by Weight nitrocellulose, 29.2% sorbed toluene and 0.8% water, and had a bulk density, dry basis, of 21.7 pounds per cubic foot. The toluene-wet particles of nitrocellulose flowed freely over each other and retained their sorbed toluene content on storage in a closed container without an objectionable amount of sorbed toluene being lost by gravity drainage.

The fibrous nitrocellulose employed in this example wasin the form of relatively uniformly sized fiber aggregate particles obtained by nitrating cellulose fiber aggregate particles prepared by cutting sheets of pulp board into particles approximately inch x inch x inch in dimension. These cellulose fiber aggregate particles were not materially changed in physical form or dimension during nitration thereof.

The ASTM inch falling ball viscosity characteristic of the nitrocellulose was measured on a 12.2% by Weight solution of the nitrocellulose in a solvent composed of 55% toluene, 25% denatured ethyl alcohol, and 20% ethyl acetate by weight at 25 C., noting the time in seconds for a inch steel ball to fall freely ten inches through the solution.

EXAMPLES 2-10 A series of toluene-wet, smooth, hardened, densified nitrocellulose granular products were prepared following substantially the same procedure described in Example 1. In these examples, methyl isobutyl ketone was employed in place of the methyl ethyl ketone in Example 1 to alter the physical form of the nitrocellulose. Table 1 following presents pertinent data relative to the nitrogen content and viscosity characteristic of the nitrocellulose, weight of fibrous nitrocellulose in the aqueous nitrocellulose slurry, parts of solvent for each part by weight of nitrocellulose, temperature in the slurry when solvent was added, temperature at the end of azeotropic distillation of the solvent at atmospheric pressure from the aqueous nitrocellulose slurry, bulk density of the altered form of the nitrocellulose particles following solvent treatment and removal, reduced pressure applied for azeotropic distillation displacement of sorbed Water by toluene, temperature in the toluene slurry of nitrocellulose at the beginning and end of azeotropic distillation displacement of sorbed water by toluene, bulk density of the toluene-wetted nitrocellulose product, and composition of the final toluene-wet nitrocellulose product in terms of nitrocellulose content, sorbed toluene content, and residual water remaining in the product.

Table 2 follow- Bulk Density of Nitrocellulose After Solvent Treatment and Removal, lbs/cu. it., Dry Basis Residual Water,

Sorbed Toluene, Percent by Weight Percent by Weight Toluene-Wet Nitrocellulose Product Nitro-cellulose Content, Percent by Weight Bulk Density,

lbs./cu.ft, Dry Basis ing presents the same kind of pertinent data relative to these examples that Table 1 presents for Examples 2-10,

Concentration of Nitrocellulose in Aqueous Slurry, Percent by Weight Temperature in Toluene Slurry at End of Distillation, C.

Temperature in Toluene Slurry at Beginning of The fibrous nitrocellulose employed in these examples Was in the same form of fiber aggregate particles as described in Example 1.

9 w o L 5 3 m Iah u 6B d H 1 n 688866868 6 /EV. c n m 644466464 0 hs t hlo t s .1 N FB A V t M1 n m h MY CY 555555555 E 1 111 L.L1 1 L Qt 111111111 Gun 09 1c a NP 1 Coutrolno alteration of physical form of nitrocellulose. 2 Insuificient alteration of physical form of nitrocellulose.

40 A series of toluene-Wet, smooth, hardened, densrfied nitrocellulose granular products were prepared, follow- The No.

With the addition of data on reduced pressure applied for azeotropic distillation of solvent from the aqueous slurry E of nitrocellulose. ple 1, with the exceptions that the solvent employed t The physical form of the fibrous nitrocellulose emaltcr the physical form of the nitroc ployed in these examples was the same as described in isobutyl Example 1.

ing substantially the same procedure described in ellulose was methyl 5O ketone instead of methyl ethyl ketone, and the Table 2 u 3 S mmmmmw h CMMTQT D. 111146931 7 D mm Ma 8 6 6 5 6 7 1 1 :a i fl 9. 2229.239. 2 i m u eu Bo S a u V. w mf Q m mmDmmu t 1 S n 1 74 54381 518 15 W mu m w 8888788 S88E88 0 t r 0 et u TuaoH .1 q Sfi S N A m & e m real y 0 S r 0 Ptmrflsmumu F 5fO0OO55 D5- u5555 1 w re 5 &&0 9 7 &&4 &L&6 4 a u Dnnqm 1111 11111111 .m dm m WA f 5 eumt 0 w R l P t f 0 m5 n mwm O 8 1d .1 o t U d 55755558 556 m WQU A 444 44444MQ4446 e Au o t m 1C% 1 VmV A T I w t m mm mb t li no- 68288866688446 mwamw oorooooooododo lPr o Rb s N st H UH .m.m%%t t h adufl flmq m 88811100000077 n A tttaaaaaaaaaaa e. ny 11111111 lIy n O M C 1 .S e w mwfu m w nnhm H MVC 66604804666686 m F w fiamnunmLd nmLfififinud b 0 qte 2 2 r M MS H An 0 N I C m t e 09% nu 55555555555555 WVPV LLLLLLLLLLLLLL 0 11111111111111 nm .1 h t n O N x E l 1 Table 2Continued Displacement of Sorbed Water by Toluene Toluene-Wet Nitrocellulose Product Reduced Pressure Ex. Applied for Distil- Temperature in Temperature in No. lation of Water Toluene Slurry at Toluene Slurry at Bulk Density, Nitrocellulose Sorbed Toluene, Residual Water, from Toluene Beginning of Endof Distillalbs/cu. ft, Content, Percent Percent by Weight Percent by Weight Slurry of Water-Wet Distillation, C. tlon, C. Dry Basis by Weight Nitrocellulose,

Inches of Mercury 19. 5 50 7O 19. 2 66 33. 6 0. 4 16. 5 63 84 24. 9 65 34. 5 0. 5 17. 5 46 74 30. 9 74 23. 8 2. 2 l8. 5 59 80 32. 1 77 22.7 0.3 18. 5 48 78 25. 5 72 27. 8 0. 2 19. 55 82 24. 79 20. 4 0. 6 17. 5 63 83 29.9 68 31. 8 l). 2 16. 5 63 85 26. 6 67 32. 8 0. 2 l8. 5 62 83 30. 7 69 30. 8 0.2 18. 5 63 78 28. 8 75 24. 0 1. 0 17. 5 62 78 33. 7 75 23. 8 1. 2 17. 5 50 78 20. 2 64 35. 8 0. 2 16. 5 62 82 22, 9 65 34. 9 0. 1 17. 5 66 84 30. 4 69 30. 6 0. 4

EXAMPLES -31 A series of toluene-wet, smooth, hardened, densified nitrocellulose granular products were prepared following substantially the same procedure described in Example 1,

picked cotton linters. The fibrous nitrocellulose employed in Example 31 was in the same form of fiber aggregate particles as described in Example 1. The viscosity characteristic of the nitrocellulose employed in Examples 25,

except that methyl isobutyl ketone was employed in Exi 30.and .3 i f ws i i llgxamp 1e amples 2530, and isopropyl acetate was employed in vlscosl y c arac ens 1c 0 e m roce u 056 m Example 31, in place of the methyl ethyl ketone of Exployeq i Examples 27 e 28 was measured on solunon ample l, to alter the physical form of the nitrocellulose. i f g Paras 20 parts denature? The fibrous nitrocellulose starting materials employed in at y O Parts 0 acetorne P Welght at 25 Examples 25 28 were in the form of loose bulk fibers C., noting the time 1n seconds for a V lIlCh steel ball to obtained by nitrating picked cotton linters. The fibrous fan freely ten i through the nitrocellulose starting material employed in Examples 29 Table 3 followlng Presents same klnd 0f Pertlnent a d 30 wa ble l o in the form of loose b lk fib data relative to these examples that Table 1 presents for obtained by nitrating shredded wood pulp instead of Examples 2-10.

Table 3 Nitrocellulose Alteration of Physical Form of Nitrocellulose Temperature in Bulk Density of No. 5/16 Inch Concentration of Parts of Solvent Temperature in Aqueous Slurry Nitrocellulose Nitrogen Content. Falling Ball Nitrocellulose per Part of Aqueous Slurry at End of Solvent Aftcr Solvent Percent By Weight Viscosity Char. in Aqueous Slurry, Nitrocellulose at Which Solvent Distillation from Treatment and Seconds Percent by Weight by Weight Was Added, C. the Slurry, C. Removal, lbs/cu.

it, Dry Basis 25 11. 0 6. 2 10 1. O 74 94 24. 1 26 11. O 6. 2 l0 1. 5 74 94 25. 8 27 12. 6 9. 8 10 1. 0 74 94 22. 6 28 12. 6 9. 8 10 2. 0 74 94 25. 7 29 12. 0 5. 3 10 0. 6 74 94 23. 3 30 12. 0 5. 3 10 0. 8 74 94 29. 3 31".. 11.5 4.6 10 1.0 86 29.3

Displacement of Sorbed Water by Toluene Toluene-Wet Nitrocellulose Product Reduced Pressure Ex. Applied for Distil- Temperature in Temperature in No. lation of Water Toluene Slurry at Toluene Slurry at Bulk Density, Nitro-cellulose Sorbed Toluene, Residual Water,

from Toluene Beginning of End of Distillalbs/cu. it, Content, Percent Percent by Weight Percent by Weight Slurry of Water-Wet Distillation, C. tion, 0 Dry Basis by Weight Nitrocellulose, In. of Mercury EXAMPLE 32 An aliphatic hydrocarbonavet, smooth, hardened, densified nitrocellulose granular product was prepared following substantially the same procedure described in Example 1, with the following exceptions:

(1) Methyl isobutyl ketone was employed in place of the methyl ethyl ktone of Example 1 to alter the physical form of the nitrocellulose;

(2) the solvent was removed from the aqueous slurry of nitrocellulose by azeotropic distillation under reduced pressure instead of at atmospheric pressure as in Example 1; and

(3) an aliphatic hydrocarbon having a boiling range of 247 F.-287 F. (American Mineral Spirits Super N aphtholite) was employed to displace sorbed water from the densified nitrocellulose granules in place of the toluene of Example 1.

Table 4 following presents the same kind of pertinent data relative to this example that Table 2 presents for Examples 1124.

The physical form of the fibrous nitrocellulose employed in this example was the same as described in Example l.

Table Generally, nitrocellulose-water slurries containing from about 5% to about 20% by weight of fibrous nitrocellulose have been employed, and preferably from about to about by weight of nitrocellulose. Although slurry consistencies of any concentration of nitrocellulose below about 5% by weight can be employed, it is not presently considered to be economical to do so. As noted above, the upper practical limit is governed by the ability to agitate the slurry effectively, and for some physical forms of fibrous nitrocellulose this upper practical limit can be appreciably higher than by weight of fibrous nitrocellulose in the slurry. For example, the fibrous nitrocellulose to be densified may be jordaned, or ground in a ball mill, or otherwise comminuted, if desired, and such comminution makes it possible to increase the quantity of nitrocellulose which can be effectively agitated in the slurry. Generally, somewhat smaller desified particles are produced when jordaned or otherwise comminuted fibrous nitrocellulose is employed. It will be understood, however, that jordaning, or otherwise comminuting fibrous nitrocellulose is not necessary for the practice of this invention.

In accordance with a critical feature of this invention Nitrocellulose Alteration of Physical Form of Nitrocellulose Concentration of Nitrocellulose in Aqueous Slurry, Percent by Weight its Inch Falling Ball Viscosity Characteristic Seconds Nitrogen Content, Percent by Weight Parts of Solvent Per Part of Nitrocellulose, by Weight Reduced Pressure Applied for Distillation of Solvent from Aqueous Slurry, In. of Mercury Temperature in Aqueous Slurry at End of Solvent Distillation from Aqueo uiJ Slurry,

Temp. in Aqueous Slurry at Which Which Solvent Was Added, C.

Displacement of Sorbed Water by Aliphatic Hydrocarbon Aliphatic Hydrocarbon-Wet Nitrocellulose Product Reduced Pressure Applied Temperature in Temperature in for Distillation of Water Aliphatic Hydro- Aliphatic Hydro- Bulk Density Nitrocellulose Sorbed Aliphatic Residual Water, from Aliphatic Hydrocarbon Slurry at carbon Slurry at lbs/cu. ft., Dry Content, Percent Hydrocarbon, Percent by Weight carbon Slurry oi Water- Beginning of End of Distilla- Basis by Weight Percent by Weight Wet Nitro-cellulose, Distillation, 0. tion, C

Inches of Mercury The smooth, hardened, densified hydrocarbon-wet nitrocellulose granules of this invention can be produced from any fibrous nitrocellulose, obtained by nitrating natural or artificial cellulose fibers, such as cotton, purified cotton linters, purified wood pulp, regenerated cellulose fibers, and the like, in such forms as picked linters, shredded wood pulp, flufied bulk linters, finely ground or cut fibers, fiber aggregate particles, and the like. A particularly preferred form of fibrous cellulose for the purposes of this invention is prepared by cutting pulp board or linter board sheets into relatively uniformly sized fiber aggregate particles which are not materially changed in physical form or size during nitration thereof.

Substantially all commercial types and grades of fibrous nitrocellulose are suitable for the purposes of this invention, having nitrogen contents from about 10.9% to about 13.5% nitrogen by weight, and of any viscosity characteristic from the very low viscosity 1O centipoise type to exceedingly high viscosity types as exemplified by dynamite grade nitrocellulose.

In a preferred embodiment for practice of this invention, water-wet fibrous nitrocellulose, after conventional treatments for stabilization and viscosity adjustment, is mixed and agitated with a large quantity of water to produce an aqueous slurry of nitrocellulose. From an economic viewpoint is is desirable to employ slurries containing as much fibrous nitrocellulose as practicable, and the upper practical limit of nitrocellulose in the slurry is governed by the ability to agitate the slurry effectively.

the fibrous nitrocellulose is contacted with agitation in the aqueous slurry with an amount of nitrocellulose solvent sufiicient to change the physical form of the nitrocellulose from fibrous to partially colloided irregular particles or granules, having a degree of densification corresponding to a bulk density between about 20 and about 40 pounds per cubic foot, dry basis, and having a physical structure capable of holding between about 10% and about 40% by weight of sorbed hydrocarbon liquid, upon removal of the treating solvent.

Preferably the aqueous slurry of nitrocellulose should be heated to a temperature at or near the boiling point of the nitrocellulose solvent or water-solvent azeotrope prior to contacting the fibrous nitrocellulose with the solvent. Subsequent solvent removal is thus speeded markedly.

Solvents suitable for use in practicing this invention are those having an active solvent power for nitrocellulose, and preferably having an appreciable vapor pressure at or below the boiling point of water. The most useful solvents are those which have limited solubility in water and which form a minimum boiling azeotropic mixture with water. The presence of two liquid phases, however, is not required for preparing the products of this invention, although two phases may be present, if desired. Suitable solvents include, by way of example but not in limitation of the invention, various ketones such as methyl ethyl ketone, methyl propyl ketone, methyl isobutyl ketone, and the like; and various esters such as methyl acetate, ethyl acetate, propyl acetate, butylacetate, ethyl propionate, ethyl butyrate, isopropyl butyrate, and the like. Ketones, such as methyl isobutyl ketone, methyl ethyl ketone,methyl isopropyl ketone, and the like, are especially preferred for the purposes of this invention, since, in addition to having a limited solubility in water and forming minimum boiling azeotropic mixtures with.

sists of smooth, hardened, densified, irregularly shaped particles of nitrocellulose. Too little solvent leaves the physical form of the nitrocellulose unaltered or not sulficiently altered, thus resulting in a product having an excessive sorptive capacity for hydrocarbon liquid. Too muchsolvent causes excessive gelling of the nitrocellulose, thus resulting in a product having a deficient sorptive capacity for hydrocarbon liquid. As pointed out above, thedesired degree of alteration of the physical structure of the nitrocellulose is to obtain a product which has a sorptive capacity for hydrocarbon liquid between about and about 40% by Weight of hydrocarbon liquid, preferably between about and about by weight, and still more preferably between about 20% and about-25% by weightbased on total weight of the hydrocarbon-wetted nitrocellulose product, andhav ing a bulk density between about 20 pounds per cubic foot and about pounds per cubic foot, dry basis.

Solvent requirement to obtain .this objective is dependent on such factors as slurry consistency, initial physical form of the nitrocellulose, temperature, degree of agitation, and the particular solvent chosen for altering the physical form of the nitrocellulose. In general, however, it has been found that an amount of solvent between about 0.3 pound and about 2 pounds, and preferably between about 0.4 pound and 1.5 pounds per pound of nitrocellulose, dry weight, is suflicient to achieve the desired degree of alteration of the physical structure of the nitrocellulose for the purposes of this invention. It has also been found that under any particular selected set of conditions that the degree of alteration of the physical structure of the nitrocellulose increases with increasing quantity of active nitrocellulose solvent employed, irrespective of the solvent selected, and this factor predominantly provides a positive basis for control of the degree of alteration of the physical structure of the nitrocellulose. Hence, with any particular selected nitrocellulose solvent, it is a simple expedient to carry out a preliminary trial run, employing an amount of solvent within the above-indicated useful range of solvent quantities, and determine the sorptive capacity of the resulting nitrocellulose product for hydrocarbon liquid. It is then a simple matter in subsequent runs to increase or decrease the amount of solvent to obtain the physical structure having the desired sorptive capacity for hydrocarbon liquid.

The solvent treatment for altering the physical structure of the nitrocellulose can be accomplished by addi tion of the solvent to an agitated slurry of fibrous nitrocellulose in water, by addition of fibrous nitrocellulose to an agitated mixture of water and solvent, or by simultaneous addition of all ingredients, with agitation, as in a continuous process. Moreover, it has been found that softening of the nitrocellulose fibers by the active nitrocellulose solvent occurs very rapidly upon bringing the nitrocellulose and solvent into contact with each other in In this process the tiny fibrous projections the aqueous slurry. Accordingly, it is important to maintain vigorous agitation in the aqueous slurry from the moment that the nitrocellulose is contacted by the active solvent in the aqueous slurry until the softened nitrocellulose particles have been hardened by removal of substantially all of the solvent. Agitation prevents substantial agglomeration of the softened nitrocellulose particles into lumps, and should be sufiiciently vigorous at all times to keep the nitrocellulose uniformly distributed throughout the slurry.

Any desired additives, such as nitrocellulose stabilizers,

plasticizers, and the like, which are soluble in the solvent employed to alter the physical form of the nitrocellulose and which are insoluble in water canbe introduced with the solvent and become very uniformly distributed into the nitrocellulose during alteration of the physical form of the nitrocellulose in accordance with this invention.

Hardening of the softened nitrocellulose is carried out by boiling off the solvent until substantially all solvent is removed from the nitrocellulose, and this may be accomplished at atmospheric pressure, under vacuum, or under pressure, as desired. This may require from about 20 minutes to about 4 hours, depending upon equipment used and the solvent which has been employed. Vacuum distillation is preferred, since distillation temperatures are lower than with atmospheric or pressure distillation and usually requires less time.

Following solvent removal, excess water is separated from the resulting hardened densified nitrocellulose particlcs by any convenient means, such as gravity drain age, suction, centrifugation, or the like, and sorbed water remaining in and on the nitrocellulose after such drainage is displaced by distillation in the presence ofan excess of volatile hydrocarbon liquid. For this purpose, it is convenient simply to suspend or slurry the water-wet ment of sorbed water from the nitrocellulose by hydrocarbon liquid. The resulting hydrocarbon-wet nitrocellose may, and usually does, contain a small residuum of sorbed water, usually substantially less than 1% by weight of the final product. Such residuum of sorbed water may, however, be on the order of 1 to 4% by weight of the final product, preferably less than 2%, without significant interference with use of the hydrocarbonwet nitrocellulose in lacquers, protective coatings, adhesives, inks, and the like.

Any volatile hydrocarbon which is liquid at ordinary temperatures and atmospheric pressure may be employed for the purposes of this invention including aliphatic, cycloaliphatic, aryl, aralkyl and alkaryl hydrocarbons. In short, any conventional hydrocarbon or hydrocarbon mixture commonly employed in nitrocellulose compositions is suitable. Preferably, the hydrocarbon should have an appreciable vapor pressure at or below the boiling point of water and the most useful hydrocarbons form minimum boiling azeotropic mixtures with water, although this is not necessary for practice of the invention. Some typical hydrocarbon liquids include, by way of example, heptane, octane, isooctane, petroleum spirits, mineral spirits, gasoline, various proprietary petroleum distillate cuts, cyclopentane, cyclohexane, methyl cyclohexane, benzene, toluene, xylene, ethyl benzene, styrene, a-methyl styrene, various proprietary aromatic hydrocarbon distillate cuts, and the like. Toluene is a particularly desirable hydrocarbon for the purposes of this invention because of the very wide use of this diluent in nitrocellulose compositions.

Following displacement of sorbed water from the nitrocellulose particles by hydrocarbon liquid, excess hydrocarbon liquid is then separated from the resulting hydrocarbon wet nitrocellulose product by any convenient 13 means, such as gravity drainage, centrifugation, suction, or the like. It has been found that substantially all of the excess hydrocarbon liquid drains off freely by gravity within a period of 1 to 2 hours to produce a product uniformly wet with the desired amount of sorbed hydrocarbon liquid within the range between about and about 40% by weight, based on total weight, without having to resort to the costly and hazardous use of hydraulic presses to reduce the volatile content to the desired level, as in necessary in conventional dehydration practice with fibrous nitrocellulose. Fibrous nitrocellulose in loose bulk form which has not had its physical form altered by the process of this invention has been found upon gravity drainage to retain between about 55% and about 60% by weight of sorbed hydrocarbon liquid based on total weight of hydrocarbon-wet nitrocellulose, and thus must be subjected to hydraulic pressing to reduce the volatile content to an acceptable level.

In this respect, therefore, the present invention provides a distinct advantage over conventional dehydration practice.

The products of this invention can be loaded into shipping containers as soon as excess hydrocarbon liquid has been separated by drainage, centrifugation, or the like. Since the hydrocarbon-wet nitrocellulose particles of this invention flow freely over each other without any substantial tendency to cling together, they can be readily discharged from shipping and storage containers simply by pouring the product from the container. Fibrous nitrocellulose, by contrast, clings together and must be laboriously forked out of the shipping container.

Moreover, the higher bulk density of the hydrocarbonwet densified nitrocellulose products of this invention afford transportation savings over conventional fibrous nitrocellulose. Fibrous nitrocellulose has a loose bulk density of about 12 to 13 pounds (dry basis) per cubic foot. By contrast, the product of this invention, having a bulk density between about 20 pounds and about 40 pounds (dry basis) per cubic foot, permits substantially heavier .barrel loadings.

Additionally, it has been found that the products of this invention dissolve in lacquer solvents more rapidly than conventional fibrous nitrocellulose because there is substantially no tendency for the smooth, hardened, densified particles to agglomerate into large lumps, as is the case with fibrous nitrocellulose. The poorer the agitation, the greater is the advantage of the densified nitrocellulose particles of this invention.

The hydrocarbon-wet nitrocellulose products of this invention can be used in any application where commercial nitrocellulose is now used, such as lacquers, plastics, paints, adhesives, coatings, inks, irnpregnations, propellants, and the like.

What we claim and desire to protect by Letters Patent is:

1. A process for preparing hydrocarbon-wet nitrocellulose which comprises (a) contacting a slurry of fibrous nitrocellulose with agitation in a heated aqueous bath with an organic liquid solvent which has active solvent power for said nitrocellulose;

(b) regulating the amount of said solvent between about 0.3 part and about 2 parts by weight per part of nitrocellulose to soften and destroy the fibrous structure of said nitrocellulose without dissolution of said nitrocellulose;

(c) removing substantially all of said solvent by dis tillation while continuing agitation to transform the softened nitrocellulose into smooth, hardened, densified, irregular granules having a free-draining physical structure capable of holding between about 10% and about 40% by weight of sorbed nonsolvent liquid;

((1) separating excess water from the resulting hardened nitrocellulose granules to produce nitrocellulose granules wet with sorbed water;

(6) thereafter substantially displacing sorbed water from the water-wet nitrocellulose granules by distillation in the presence of an excess of volatile hydrocarbon liquid;

(f) separating excess hydrocarbon liquid; and

(g) recovering nitrocellulose granules wetted with between about 10% and about 40% by weight of sorbed hydrocarbon, based on total weight.

2. The process in accordance with claim 1 in which the amount of said organic liquid solvent is regulated between about 0.4 part and about 1.5 parts by weight per part of nitrocellulose.

3. The process in accordance with claim 1 in which the organic liquid solvent is a ketone.

4. The process in accordance with claim 3 in which the ketone solvent is methyl isobutyl ketone.

S. The process in accordance with claim 1 in which the organic liquid solvent is an ester.

6. The process in accordance with claim 1 in which the volatile hydrocarbon liquid is an aromatic hydrocarbon.

7. The process in accordance with claim 6 in which the aromatic hydrocarbon is toluene.

8. The process in accordance with claim 1 in which the volatile hydrocarbon liquid is an aliphatic hydrocarbon.

9. The process in accordance with claim 1 in which the organic liquid solvent is removed by distillation at atmospheric pressure.

10. The process in accordance with claim 1 in which the organic liquid solvent is removed by distillation at reduced pressure.

11. The process in accordance with claim 1 in which sorbed water is substantially displaced from the water wet nitrocellulose granules with hydrocarbon by distillation in the presence of an excess of volatile hydrocarbon liquid at reduced pressure.

12. The process in accordance with claim 1 in which the fibrous nitrocellulose is in the form of relatively uniformly sized fiber aggregate particles.

13. The process in accordance with claim 1 in which the fibrous nitrocellulose is in the form of loose, bulk fibers.

14. Smooth, hard, densified, irregular nitrocellulose particles wet with between about 10% and about 40% by Weight of sorbed hydrocarbon liquid, based on total weight, and having a bulk density between about 20 pound per cubic foot and about 40 pounds per cubic foot, dry basis, said particles being free-flowing, fast dissolving, and relatively incompressible.

References Cited by the Examiner UNITED STATES PATENTS BENJAMIN R. PADGETT, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 284 253 November 8 1966 John G. Enders et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 35, for "7/32" read 1/32 Signed and sealed this 12th day of September 1967.

(SEAL) Attest:

ERNEST W. SWIDER Attcsfing Offioer EDWARD J. BRENNER Commissioner of Patents 

1. A PROCESS FOR PREPARING HYDROCARBON-WET NITROCELLULOSE WHICH COMPRISES (A) CONTACTING A SLURRY OF FIBROUS NITROCELULOSE WITH AGITATION IN A HEATED AQUEOUS BATH WITH AN ORGANIC LIQUID SOLVENT WHICH HAS ACTIVE SOLVENT POWER FOR SAID NITROCELLULOSE; (B) REGULATING THE AMOUNT OF SAID SOLVENT BETWEEN ABOUT 0.3 PART AND ABOUT 2 PARTS BY WEIGHT PER PRT OF NIROCELLULOSE TO SOFTEN AND DESTROY THE FIBROUS STRUCTURE OF SAID NITROCELLULOSE WITHOUT DISSOLUTION OF SAID NITROCELLULOSE; (C) REMOVING SUBSTANTIALLY ALL OF SAID SOLVENT BY DISTILLATION WHILE CONTINUING AGITATION TO TRANSFORM THE SOFTENED NITROCELLULOSE INTO SMOOTH, HARDENED, DENSIFIED, IRREGULAR GRANULES HAVING A FREE-DRAINING PHYSICAL STRUCTURE CAPABLE OF HOLDING BETWEEN ABOUT 10% AND ABOUT 40% BY WEIGHT OF SORBED NONSOLVENT LIQUID; (D) SEPARATING EXCESS WATER FROM THE RESULTING HARDENED NITROCELLULOSE GRANULES TO PRODUCE NITROCELLULOSE GRANULES WET WITH SORBED WATER; (E) THEREAFTER SUBSTANTIALLY DISPLACING SORBED WATER FROM THE WATER-WET NITROCELLULOSE GRANULES BY DISTILLATION IN THE PRESENCE OF AN EXCESS OF VOLATILE HYDROCARBON LIQUID; (F) SEPARATING EXCESS HYDROCARBON LIQUID; AND (G) RECOVERING NITROCELLULOSE GRANULES WETTED WITH BETWEEN ABOUT 10% AND ABOUT 40% BY WEIGHT OF SORBED HYDROCARBON, BASED ON TOTAL WEIGHT. 